Vacuum Pumps

The Crucial Role of Vacuum Pumps in Evaporation and Freeze Drying

What is Vacuum and Pressure Reduction?

• Defining “Vacuum”: Is it truly empty?
  Many people associate the word “vacuum” with a state of “absolute emptiness.” However, in a scientific and industrial context, a vacuum is not an empty space but simply a state where the gas is highly rarefied.
  At sea level, the standard atmospheric pressure is approximately 1013hPa. As you climb a high mountain, the air becomes thinner; at the altitudes where airplanes fly, it is even more sparse. The outer space where the International Space Station orbits is what we typically call a “vacuum.”
  
  
• The Official Definition (JIS Standards)
  According to the Japanese Industrial Standards (JIS), a vacuum is formally defined as: “A state of a space filled with gas at a pressure lower than the normal atmospheric pressure.” Therefore, the process of creating this state—lowering the pressure below the ambient atmospheric level—is what we call “Pressure Reduction”.

The Reality of Vacuum: It is never “Zero”
Currently, it is physically impossible to create an “absolute vacuum” where nothing exists, regardless of the technology used. Even in the highest vacuum levels achievable by human engineering, millions of gas molecules remain in a 1L vessel. In fact, it is believed that there is no space in the universe that is truly “empty.”

• High Vacuum / “Good” Vacuum:
  The lower the pressure value (Pa), the higher the vacuum degree. This means there are fewer gas molecules remaining in the space.
• Low Vacuum / “Poor” Vacuum:
  The higher the pressure value (Pa), the lower the vacuum degree. The state is closer to normal atmospheric pressure.

Units of Pressure and Vacuum Levels

The International System of Units (SI) for pressure is the Pascal (Pa). Other commonly used units include mmHg (millimeters of mercury), Torr, atm (standard atmosphere), and bar. The conversion rates are as follows:

1 Pa = 7.501×10⁻³mmHg = 7.501×10⁻³Torr = 9.869×10⁻⁶atm = 1×10⁻⁵bar

Historically, “mbar” (millibar) was used in weather forecasting to measure atmospheric pressure for systems like low-pressure areas and typhoons. Following the 1992 amendment of the Measurement Act, “mbar” was replaced by “hPa” (hectopascal). Since 1 mbar = 1hPa, the numerical values remain the same despite the change in unit designation.

Equipment Types, Pump Categories, and Vacuum Ranges

Rotary Evaporator
This is the most common device used to remove solvents and moisture through distillation.

Freeze Dryer (Lyophilizer)
This device removes moisture from a product by freezing it and then sublimating the ice into vapor. In recent years, it has been utilized in a wide range of fields, with various specialized systems being developed, such as spray freeze-drying granulation systems.

• Oil Diffusion Pump
  A vacuum pump that heats oil with a heater to generate vapor, which is then ejected at high velocity through a nozzle; the resulting vapor jet entrains and transports gas molecules to create a vacuum.
• Turbo molecular pump
  A vacuum pump that achieves high vacuum by alternately stacking stationary blades and high-speed rotating blades, which drive gas molecules in a single direction through momentum transfer.
• Cryopump
  A vacuum pump that creates an extremely low-temperature surface inside the vacuum chamber, where gas molecules are condensed and captured to achieve evacuation.

How to Select the Right Vacuum Pumps

[Point 1] What level of ultimate pressure (vacuum level) is required?

The required pressure (vacuum level) varies depending on the application.
Referring to the “Equipment Types, Pump Categories, and Vacuum Ranges” chart above, identify which type of vacuum pump is suitable for your specific needs.

[Point 2] Which type is better: “Oil” or “Dry”?

Oil Pumps: If high vacuum levels are your priority and you are not concerned about oil maintenance, oil pumps are the preferred choice for achieving a high vacuum.
Dry Pumps: If you must avoid oil mist and require a clean environment, a dry pump is essential for maintaining a contaminant-free atmosphere.

[Point 3] How long will the evacuation take?

The required pumping speed is calculated based on the volume of the vessel to be evacuated and the desired evacuation time.

[Point 4] What type of gas (solvent) will be evacuated?

Vacuum pumps are available in different material specifications, such as Standard (aqueous/water-based) or Chemical-resistant (corrosion-resistant).
It is essential to verify the compatibility of the pump specifications based on the type of gas and the corrosiveness of the substances being evacuated.

Additional selection criteria include price, installation space, and power requirements.

Structure and Features of Major Vacuum Systems

Pressure Ranges by Pump Type (Non-Exponential Notation)
To help you choose the right pump, here is a comparison of typical pressure ranges using standard numerical values (Pa).

Maintenance Tips and Best Practices

• Maintenance Alert: Change the Vacuum Pump Oil Regularly!
  The oil within an Oil-Sealed Rotary Vacuum Pump gradually degrades with use. As it becomes contaminated with moisture and solvents, changes in its concentration, viscosity, and vapor pressure, along with chemical changes due to heat build-up, will impair the internal sealing performance. This directly affects the ultimate pressure the pump can achieve.
  Furthermore, the accumulation of rust and sludge can lead to serious mechanical failures. It is essential to perform periodic oil changes, using oil color and deterioration of vacuum levels as key indicators for maintenance.
• Oil-Sealed Rotary Vacuum Pump Stand: Model OPM-1000
  Eliminate the hassle of maintenance with our specialized stand. OPM-1000 allows you to tilt the vacuum pump easily, enabling smooth oil changes without worrying about the unit’s heavy weight.
  Equipped with heavy-duty casters, it also allows you to move pumps—which are often tucked away in corners or behind other equipment—without the need for heavy lifting.

How to Use the Movable Rack for Oil Rotary Vacuum Pumps

This movable rack significantly reduces the burden of oil change

• By using this special rack, oil can be changed without worrying about the weight of vacuum pumps.
• To make it easier to drain the oil, the rack on which the oil rotary vacuum pump is mounted can be tilted by 30° angle.
• Equipped with casters, the oil rotary vacuum pump can be moved without lifting, even when placed in corners or hidden areas.